DESCRIPTION (Applicant?s Abstract): Arabidopsisis is uniquely poised to address the role of DNA in centromere activity. The five Arabidopsis centromeres have been mapped, two centromeres regions sequenced, and by the end of 2000 the other three will be complete. The experiments described in this proposal will test the function of DNA fragments residing within the Arabidopsis centromere, measuring their capacity to direct chromosome transmission. To this end a specially designed set of vectors will be used to test large DNA fragments from the Arabidopsis centromere for activity both when integrated into a natural chromosome and when segregating autonomously on a minichromosome. The vectors efficiently introduce telomeres, plant tansformation elements and plant selectable markers and cell autonomous markers into centromere DNA clones. The fidelity of chromosome transmission of the centromere fragments as well as the native chromosome will be evaluated through individual meiotic and mitotic divisions with the reporter genes, which allow rapid visual screening. The work described here will broadly contribute to the understanding of aberrant chromosome segregation, which, in humans, leads to decreased fertility, spontaneous abortions and trisomy syndromes such Downs and Klinefelters.